<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 200px;
            height: 200px;
            border: 50px solid rgba(0, 0, 0, 0.5);
            padding: 50px;
            background-image: url(./assets/bk.jpg);

            /* 
            背景延伸区域
            1.border-box 边框区域
            2.padding-box 内边距区域
            3.content-box 内容区域
            */
            background-clip: border-box;
            background-clip: padding-box;
            background-clip: content-box;  
        }
    </style>
</head>
<body>
    <div class="box">

    </div>
</body>
</html>